Helically crimped fibers of poly(trimethylene terephthalate) having asymmetric birefringence

ABSTRACT

HELICALLY CRIMPED TEXTILE FIBERS OF POLY(TRIMETHYLENE TEREPHTHALATE) ARE PRODUCED BY MELT SPINNING FILAMENTS TO HAVE ASYMMETRIC BIREFRINGENCE ACROSS THEIR DIAMETERS, DRAWING THE FILAMENTS TO ORIENT THE MOLECULES THEREOF, ANNEALING THE DRAWN FILAMENTS AT 100*-190*C. WHILE HELD AT CONSTANT LENGTH, AND HEATING THE ANNEALED FILAMENTS IN A RELAXED CONDITION ABOVE 45*C. TO DEVELOP CRIMP.

United States Patent O 3,681,188 HELICALLY CRIMPED FIBERS F POLY(TRI- METHYLENE TEREPHTHALATE) HAVING ASYMMETRIC BIREFRINGENCE Max Emerson Harris, Kinston, N.C., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del. No Drawing. Original application May 10, 1969, Ser. No. 821,084. Divided and this application Feb. 19, 1971, Ser. No. 117,110

Int. Cl. D02g 1/00; Dilld 5/22 US. Cl. 161-173 1 Claim ABSTRACT OF THE DISCLOSURE Helically crimped textile fibers of poly(trimethylene terephthalate) are produced by melt spinning filaments to have asymmetric birefringence across their diameters, drawing the filaments to orient the molecules thereof, annealing the drawn filaments at l00-l90 C. while held at constant length, and heating the annealed filaments in a relaxed condition above 45 C. to develop crimp.

CROSS-REFERENCE TO' RELATED APPLICATION This is a division of my copending application Ser. No. 821,084, filed May 10, 1969, now Pat. No. 3,584,103.

FIELD OF THE INVENTION SUMMARY OF THE INVENTION The product of this invention is poly(trimethylene terephthalate) in a helically-crimped form having a Crimp Frequency of at least 3 crimps per inch and a Crimp Index of at least 40% (preferably 50% to 80%); the poly(trimethylene terephthalate) on opposite sides of the fiber being of different characteristics, one side running along the length of the fiber substantially on the inside of the helix having a lower molecular orientation and crystallinity characterized by at least 0.002 unit lower birefringence than the other side of the fiber which is substantially on the outside of the helix.

The invention also comprehends a process for imparting a helical crimp to filaments comprising poly(trimethylene terephthalate) which have an asymmetric birefringence across their diameters comprising the steps of cold drawing the filaments to orient the molecules thereof, the filaments preferably being drawn 3 -4' at 40-60 'C., annealing the drawn filaments by heating at substantially constant length until their temperature reaches from about 100 C. to about 190 C. and thereafter heating the annealed filaments in a relaxed condition at a temperature above their T temperature (about 45 C.) and preferably about 140 C. for 2 to minutes to develop crimp.

DEFINITIONS In order to facilitate an understanding of the present invention, the following is an explanation of terms and symbols used herein:

3,681,188 Patented Aug. 1, 1972 By T temperature is meant the classical glasstransition temperature, also called the second-order transition temperature of the fiber. It is the temperature at which the thermoplastic material changes from the rubbery tate to the glassy state and also the temperature at which a discontinuity occurs in a graph showing temperature as a function of a thermodynamic variable such as heat capacity. The T of poly(ethylene terephthalate) is about 60 C. and the T of poly(trimethylene terephthalate) is about 45 C.

Crimp Frequency is the number of crimps per unit length of fiber. To obtain the Crimp Frequency, the fiber is extended until the crimp substantially disappears. Marks are placed on the extended fiber at one-inch intervals. The fiber is then relaxed from extension, and the number of crimp peaks between two adjacent marks is recorded as Crimp Frequency (crimps per inch).

Crimp Index is determined by the following procedure:

From the known denier of the yarn, calculate the number of turns of a skein reel required to achieve a denier of 1500 (167 Tex) (the circumference of the reel may be any convenient length), using the formula Replace the 300-gm. weight with a 4.5 gmm. weight.

Measure the new length (L Crimp Index is determined from thee measurements given above by the formula:

CI (L lii) Intrinsic Viscosity is defined as the limit of the fraction as concentration 0 approaches zero, where r is the Relative Viscosity as defined below, except that Relative Viscostiy is measured at several concentrations to facilitate extrapolation to zero concentration, and the solvent employed in this measurement is a mixture of three parts of methylene chloride and one part of trifluoroacetic acid (by weight). A more detailed discussion of methods of measuring relative and intrinsic viscosities is given in Preparative Methods of Polymer Chemistry, Sorenson and Campbell, Interscience, 1961.

Relative Viscosity referes to the ratio of the viscosity of a 10% solution of the polymer in a mixture of 10 parts of phenol and 7 parts of 2,4,6-trichlorophenol (by weight) to the viscosity of the solvent itself, both measured at 25 C. and expressed in the same units.

BIREFRINGENCE A fiber has two refractive indices: 7 obtained with monochromatic light polarized in a plane parallel to the fiber axis and 1; obtained when the plane of polarization is perpendicular to the fiber axis. The birefringence of the :fiber is then defined as the difference between 1 and am; i.e., A 4- [Heyn, Tex. Res. J. 22, 513 1952) The refractive indices 1 and n are determined using an interference microscope which produces a banded field of parallel interference fringes. Displacement of these fringes is caused by a fiber when it is immersed in a liquid of known refractive index and placed in the microscope field. A fiber will displace an interference fringe by an amount which is proportional to its thickness and the difference in the refractive indices of the fiber and the medium. Therefore, to calculate 1 or 1;\(, it is necessary to determine the difference in refractive index between the fiber and two media of different refractive index. The pertinent equations are:

where X =difference in refractive index of fiber and medium d =displacement of interference fringe in medium 1 d =displacement of interference fringe in medium 2 =refractive index of medium 1 =refractive index of medium 2 The refractive index of the fiber is then:

If the polarization of the light is parallel to the fiber axis, then the or if perpendicular then =1;

The advantage of the interference microscopy method is that birefringence may be calculated for any specific point across the fiber image, thereby allowing one to establish a birefringence profile for a fiber.

The experimental method used is to mount a fiber on a microscope slide and immerse it in a liquid of known refractive index (Cargille Company Certified Index of Refraction Liquids). The slide is then observed in the field of the interference microscope (manufactured by Ernst Leitz, Wetzlar, Germany-Transmitted Light Interfence Microscope) using polarized light from a mercury lamp (546 m line) with the fiber oriented parallel to the plane of polarization. The refractive index of the medium should be such that a displacement of the interference fringe line is substantially less than the distance between adjacent fringes. A photograph of the image is then taken. The medium is then replaced by a second medium which produces about the same fringe displacement but in the opposite direction and a second photo graph taken. The displacement of the fringe line is then measured on each photograph at the same distance from the edge of the fiber image and expressed in each case as a fraction of the distance between fringes. This gives, then d and d of Equation 1. To obtain the refractive index profile, a series of these measurements is made across the fiber image and the refractive index calculated at each point using Equations 1 and 2. A similar sequence is followed using light polarized perpendicular to the fiber axis. Measurements are made at the same distances across the fiber as were made when the light was polarized parallel to the fiber axis. The birefrigence at each point can be readily calculated once 1 and 1 are known. It is not necessary to measure the thickness of the fiber at any of the points where fringe displacement is determined because thickness cancels out in the derivation of Equation 1.

DETAILED DESCRIPTION OF THE INVENTION The advantage of the present invention; i.e., a crimped fiber of poly(trimethylene terephthalate), having high Crimp Frequency and high Crimp Index, is obtained when a fiber of poly (trimethylene terephthalate), having asymmetric birefringence across its diameter, is annealed at constant length subsequent to drawing and thereafter relaxed in heat. This behavior is entirely unexpected because the same poly(trimethylene terephthalate) fiber having the same asymmetric birefringence and having been drawn in the same manner but having been given no taut annealing treatment subsequent thereto develops substantially less crimp upon relaxation in heat. This unusual behavior is even more surprising in view of the fact that a fiber of the homologue poly(ethylene terephthlate) having asymmertic birefringence across its diameter develpos no substantial crimp upon the same relaxation-in-heat treatment if it had been given the same annealing treatment subsequent to drawing.

The fibers of the present invention are two-sided, each side running longitudinally of the fibers. The molecules of one side are more oriented than the molecules of the other side; hence they exhibit differential birefringence. In the helical poly(trimethylene terephthalate) fiber, the side with lower orientation is on the inside of the helix and the side with higher orientation is on the outside of the helix; in fibers of poly(ethylene terephthalate) having asymmetric birefringence the reverse is true. The birefringence of the polymer on the inside of the helix of the fibers of the present invention is at least 0.002 unit lower than the birefringence of the polymer on the outside of the helix.

Although not wishing to be limited or bound in any way by theory, it is believed that the poly(trimethylene terephthalate) molecules crystallize in a nonextended configuration and specifically to about 75% of the length of the fully extended molecules (the term fully extended molecule comprehends the actual bond angles and lengths and does not mean the molecules are lined-up in a straight line), whereas poly(ethylene terephthalate) molecules crystallize in the fully extended configuration. These phenomena relate to the degree of molecular orientation in the fiber when considering ease of crystallization. The asymmetric birefringence across the diameter of the filaments indicates a higher degree of molecular orientation on one side of the fibers than on the other and in poly- (trimethylene terephthalate) the molecules of the highly oriented side (more molecularly extended) are less likely to crystallize than those of the less oriented side, whereas in poly(ethylene terephthalate) the reverse is true. The annealing treatment produces different phenomena regarding the crystalline states of poly(trimethylene terephthalate) and poly(ethylene terephthalate) and thus different shrinkage behavior in these homologues is obtained upon. such treatment.

Asymmetric birefringence, or differential birefringence as it is sometimes called, across the filament diameter may be produced by asymmetric quenching as described in Kilian US. Pat. No. 3,050,821, dated Aug. 28, 1962.

It may also be produced by contacting one longitudinal side of freshly extruded melt-spun filaments with a film of cool liquid. Other procedures to obtain this phenomenon, may be used which provide a differential of at least 0.002 unit birefringence between polymer on opposite sides of the crimped filaments.

The annealing step is essential to the successful practice of the present invention. This step follows conventional fiber-drawing procedures which usually comprise extending the fibers to from about 2 to about 8 times their original length. The yarns are preferably annealed by means of a series of hot rolls. Preferred temperatures for annealing range from about to 200 C. and the exposure of the yarn to the heat is of sufiicient duration (preferably from about 1 to 30 seconds) to raise its temperature to from about 100 C. to about C. It is important that the length of the yarn be kept substantially constant during the annealing step. No significant extension or shrinkage of the yarn is to be tolerated in the annealing step.

It should be noted that, in order to develp the full helical crimp of the new fibers, the draw-bath temperature should be related to the maximum operable draw ratio of the filaments. Preferably, the amount of orientation given the polymer molecules during extrusion from the spinneret (spin orientation) is such as to give the yarn a draw ratio of about 3X to 4x and under these conditions the draw bath should be below 70 C. and preferably 40 to 60 C. However, if the spin orientation is high so as to give a low draw-ratio, the draw-bath temperature may be above 70 C.

The full development of the helical crimp in the fibers of the present invention is realized by relaxing the fibers in heat. This step can be done before or after the fibers are made into yarn and fabrics. The temperature of this heating step is above the T of the fibers. Preferably, a temperature of about 140 C. and an exposure of from about 2 to 10 minutes is used.

The invention will be further illustrated by the following examples of preferred embodiments which are not intended to be delimitative.

EXAMPLE I Poly(trimethylene terephthalate) having an Intrinsic Viscosity of 0.8 and containing 0.1% by weight Ti is melt-spun through a standard spinneret heated to 212 C. to a 780-denier/l3-filament yarn. Wind-up speed is 600 y.p.m. (about 550 m./min.). A stream of quenching air at about 21 C. is jetted at about 27 ftF/min. (0.756 m. min.) through a 1.5 in. (9.68 cm. orifice at the filaments as they extrude from the spinneret to produce asymmetric birefringence across their diameters. The yarn is drawn 3.6x in a 50 C. water bath and subsequently annealed over rolls at 120 C., at constant length, for approximately 6 seconds. The final yarn is 237-denier/13- filament (about 18 denier per filament). The yarn is relaxed without restraint in an oven at 140 C. for 6 minutes, whereupon it develops a high degree of helical crimp. The Crimp Frequency is 7 crimps per inch (2.75 crimps/ cm.), and the Crimp Index is 73% The polymer, which is on the side of the fiber on the inside of the helix, is less oriented and less crystalline and has a birefringence of at least 0.002 unit lower as compared to the polymer on the side of the fiber which is on the outside of the helix.

EXAMPLE II Poly(trimethylene terephthalate) of 0.7 Intrinsic Viscosity and containing 0.1% by weight TiO is spun to a 4825-denier/l04-filament yarn by extruding through a spinneret heated to 240 C. containing 104 orifices each of 32 mil (0.81 mm.) diameter. The filaments are rapidly quenched asymmetrically as they emerge from the spinneret by air flowing from a radial jet having an 18.8 in. (121.3 cm?) orifice. Quench air is at 21 C. and flow is 272 ftfi/min. (7.62 m. /min.). The yarn is Wound at 448 yards per minute (410 m./min.). Twenty ends of this yarn are combined to make up a tow of 2080 filaments. The tow is drawn 3.1x in a 50 C. water-spray bath and is annealed at constant length by passing in contact with rollers in an atmosphere of 160 C., for 2.6 seconds. A lubricating and antistatic finish is then applied. The 14- denier-per-filament tow is then opened and fluifed by an air jet and passes to an oven where it is relaxed without restraint at 140 C. for 6 minutes whereupon it develops a high degree of useful helical crimp. The tow has a Crimp Index of about 52% and a Crimp Frequency of about 4 crimps per inch (1.6 crimps/cm). The fibers have' a breaking tenacity of 2.0 gms./denier at 56% elongation. Again, the polymer which is on the side of the fiber on the inside of the helix is less oriented and less crystalline and has a birefringence of at least 0.002 unit lower as compared to the polymer on the side of the fiber which is on the outside of the helix.

EXAMPLE III The same general procedure as in Example I is used with the exception that the Intrinsic Viscosity of the starting polymer is 0.94, the spinning temperature is 282 C., the air quench is at 66 ft. /min., the final yam [after drawing, annealing and relaxing (5 min. at C.)] is 5.6 denier, the draw ratio is 1.8x, the water bath is 75 C., the annealing rolls are at C., and the duration of yarn exposure to the annealing process is 26 seconds. The Crimp Index of the yarn is about 58% and its Crimp Frequency is about 6.1 crimps per inch (2.4 crimps/cm). Again, the polymer which is on the side of the fiber on the inside of the helix is less oriented and less crystalline, and has a birefringence of at least 0.002 unit lower as compared to the polymer on the side of the fiber which is on the outside of the helix.

EXAMPLE IV Example II is repeated up to the point where the twenty tow ends are combined. Instead, eight ends are combined to make up a tow (832 filaments). The tow is drawn 3.0x in a 58 C. draw bath (same aqueous composition as in Example II) and is annealed at constant length at 140 C. for 52 seconds. The tow is then relaxed in an oven for 3 minutes at 140 C. under no restraint, whereupon it develops a high degree of helical crimp. The resulting product is the Test Sample in Table I below.

For the Control Sample, the above procedure is repeated with the exception that the annealing step is omitted.

Properties of the Control and Test filaments are shown in Table I.

TAB LE I Control Test sample sample Crimp index (percent) 36 54 (Jump freqllency-erimpllnch (crimp/cm.) 3. 3(1. 30) 3. 4(1. 34) Boil-offi shrinkage (percent) 0. 4 0. 0

Birefringence:

Inside of hellx 0. 0570 0. 0535 Outside of helix 0. 0575 0. 0610 Denier per filament 15. 3 l4. 9 Tenacity (g./denler) l. 94 2. 10 Elongation (percent) 64. 6 45. s

The fibers of this invention find use in many articles of commerce such as carpets and other floor coverings, and wearing apparel.

I claim:

1. Poly(trimethylene terephthalate) textile fibers in a helically-crimped form having a Crimp Frequency of at least 3 crimps per inch and a Crimp Index of at least 40%; the Poly(trimethylene terephthalate) on opposite sides of the fiber being of different characteristics, one side running along the length of the fiber substantially on the inside of helix having a lower molecular orientation and crystallinity characterized by at least 0.002 unit lower birefringence than the other side which is substantially on the outside of the helix.

References Cited UNITED STATES PATENTS 2,465,319 3/1949 Whinfield l6ll72 2,974,391 3/1961 Speakman et a1. 2872.13 X 3,050,821 8/1962 Kilian l6l173 3,345,815 10/1967 Starkie et al l6l173 X 3,439,391 4/ 1969 DeVore et a1 2872.13 X

ROBERT F. BURNETT, Primary Examiner L. T. KENDALL, Assistant Examiner US. Cl. X.R. 

